1. Field of the Invention Relates
The invention relates to a planetary rotation piston compressor with a double-arcuate trochoidal casing track, with which a triangular piston, rotating on an eccentric shaft makes constant sliding contact at its corners, and in the housing of the compressor transfer flow pockets are provided, via which a given following working chamber, already shut off and in the vicinity of the dead center position, is connected for a short time with the compression chamber coming in front of it. Such compressors are intended especially for use in refrigeration circuits, air pressure bracking systems or as compressors in pneumatic power systems in vehicles. More particularly in the two last mentioned cases there is the requirement for the pumping of large volumes of air at a high pressure of for example up to 10 bar. Furthermore all applications require very smooth running and in this respect it is necessary to avoid the occurrence of negative torque.
2. The Prior Art
Such a negative torque arises when the compression chamber is shut off after termination of the expulsion stroke and has therefore beyond its dead center position. This negative torque leads not only to noisy running but can also even lead to breakage of the shaft owing to the build-up of torsion vibrations in the shaft.
In the German specification (Offenlegungsschrift) No. 2,402,084 these conditions are described in detail in the case of an analogous machine with a piston having two corners and a single-arcuate trochoidal track. There is a proposal in this specification to arrange the inlet and outlet ports with the distance of the longitudinal axis of the piston in order to ensure that, on passing over one of these timing ports, the pressure in the compression chamber, which has already been shut off in the vicinity of the dead center position, is relieved via these ports into the following or preceding chamber. This proposal for avoiding negative torque cannot be directly applied to the machine of the present invention having a triangular piston and a dual-arcuate casing track.
The residual volume of the working medium, which cannot be expelled owing to the unavoidable dead space of such a machine, is under a high pressure and has disadvantageous effect along the lines indicated, leads to the throughput of the machine being limited.
In accordance with the proposal of the German specification (Offenlegungsschrift) No. 2,127,546 transfer flow pockets are to be milled into the casing track in the vicinity of the piston corner delimiting the compression chamber which is being shut off and via these pockets the working medium enclosed in this chamber can partly flow into the preceding compression chamber, which, although it is also shut off, is under a lower pressure. These transfer flow pockets are to be arranged in the axial direction adjacent to each other and lands have to be left between them extending as far as the surface of the casing track in order to prevent the sealing elements of the piston corners falling into the pockets or fouling them. The pockets are therefore specifically limited in their axial extent. Furthermore in their extent in the direction of piston movement a limitation is also necessary, this limitation being due to the uncovering of the inlet port leading towards the following chamber, which then becomes the induction chamber, on further rotation of the piston. This measure is, however, not sufficient to draw off the volume of the working medium, trapped in the dead center space of the piston, into the preceding chamber, if the displacements and pressures required for the types of machines specified are to be ensured and the violent beating action, occurring at high speeds of rotation, is to be avoided which is due to negative torques, as detailed testing carried out by us has shown. This applies more especially at high speeds of rotation.
The previously proposed transfer flow pockets can furthermore only be produced at considerably expense, since milling must be carried out in the interior of the housing casing or, the transfer flow pockets lead to re-entrant mold parts. Furthermore a coating of the track, which is necessary in the case of light alloy housings, is interrupted by such recesses repeatedly in a direction perpendicular to the movement of the piston, this leading to the danger of detachment.